猫胸脊髓交感节前神经元对电刺激头端延髓腹外侧区的反应

Postsynaptic responses of thoracic sympathetic preganglionic neurons to electrical stimulation of the rostral ventrolateral medulla in cats

目的：观察电刺激猫的头端延髓腹外侧区（ＲＶＬＭ）在胸脊髓交感节前神经元（ＳＰＮｓ）上引起的反应。方法：用充灌３ｍｏｌ／ＬＫＣｌ的玻璃微电极在１１只麻醉后行人工通气猫的第３胸髓做细胞内记录，电刺激白交通支，逆行鉴定ＳＰＮｓ。结果：共记录了２４个ＳＰＮｓ，其静息膜电位为－４５～－９０ｍＶ，逆行动作电位的阈值和潜伏期分别是（２．８６±０．３７）Ｖ和（６．４８±０．８９）ｍｓ。用单个方波（０．２ｍｓ，５０～３００μＡ）刺激ＲＶＬＭ，在所有ＳＰＮｓ上都引起一组潜伏期为４～４７ｍｓ的早发快速兴奋性突触后电位（ｅＥＰＳＰｓ）；在１１个ＳＰＮｓ上还记录到一组潜伏期为７０～１４０ｍｓ的迟发ＥＰＳＰｓ（ｌＥＰＳＰｓ）。多数ｅＥＰＳＰｓ和一些ｌＥＰＳＰｓ都具有恒定的潜伏期。结论：ＲＶＬＭ的一些交感兴奋性神经元单突触地投射到胸脊髓ＳＰＮｓ上，ＲＶＬＭ的胸脊髓投射按传导速度可分为两类，即快传导和慢传导纤维，其传导速度分别是５～２５和０．７８～１．

Objective: To study the characteristics of the postsynaptic potentials in thoracic sympathetic preganglionic neurons (SPNs) evoked by electrical stimulation of the rostral ventrolateral medulla (RVLM) in cats. Methods: In 11 anesthetised, artificially ventilated cats, intracellular recordings were made from T 3 spinal cord with microelectrodes filled with 3 mol/L KCl. SPNs were identified by antidromic stimulation of the T 3 white ramus. Results: Twenty four SPNs were recorded, the resting membrane potentials of which ranged between -45 and -90 mV. The onset latency and threshold of the antidromic action potentials averaged (6.48±0.89) ms and (2.86±0.37) V, respectively. Single pulse (0.2 ms, 50～300 μA) electrical stimulation of RVLM evoked fast excitatory postsynaptic potentials (eEPSPs) with short latencies (4～47 ms) in all the 24 SPNs. In 11 of the SPNs, EPSPs with longer latencies (lEPSPs, 70～140 ms) were also recorded. Most of the eEPSPs and some of the lEPSPs were typical monosynaptic EPSPs as they were of constant onset latency. Conclusion: The results provide direct physiological evidence that some RVLM sympathoexcitatory neurons project monosynaptically to thoracic SPNs. The descending pathways from RVLM may consist of two distinct groups of fibers, of which the conduction velocities are calculated to be 5～25 and 0.78～1.60 m/s, respectively.